Encapsulation

ABSTRACT

ENCAPSULATION OF LIQUIDS WITH METAL. A CORE LIQUID IS DISPERSED IN A CARRIER LIQUID IN WHICH IT IS ESSENTIALLY INSOLUBLE (ONE OF THE LIQUID BEING AQUEOUS), IN A CONTAINER WHOSE SURFACE IS PHOBIC TO THE CORE LIQUID. METALLIZING AND REDUCING COMPOUNDS ARE ADDED. NUCLEATING METAL IS DEPOSITED AT THE INTERFACE BETWEEN THE LIQUIDS BY INTRODUCING A SURFACTANT-TYPE METAL-ORGANIC COMPOUND OF THE HYDROPHOBIC-HYDROPHILIC TYPE HAVING A MORE READILY OXIDIZABLE METAL ION THAN THE METAL OF THE METALLIZING AGENT, SO THAT MOLECULES OF THE SURFACTANT ALIGN THEMSELVES AT THE INTERFACE AND PRESENT THEIR METAL IONS TO THE AQUEOUS LIQUID TO NUCLEATE DEPOSITION OF METALLIZING IONS. IN ONE EMBODIMENT, THE METALLIZING MATERIALS, ARE DISPOSED TO DEPOSIT A NOBLE METAL AT THE INTERFACE, AND THE RESULTING NOBLE-METAL-COATED CAPSULES ARE SUBSEQUENTLY OVER-COATED WITH ONE OR MORE LAYERS OF A NON-NOBLE METAL BY ELECTRODEPOSITION.

United States Patent Oflice 3,788,955 ENCAPSULATION Nelson A. Crites andGlenn R. Schaer, Columbus, Ohio,

assignors to Battelle Development Corporation, Columbus, Ohio NoDrawing. Continuation-impart of abandoned application Ser. No. 117,059,Feb. 19, 1971. This application Oct. 7, 1971, Ser. No. 187,560

Int. Cl. B01i 13/02; C23b /56, 17/00 U.S. Cl. 204-25 26 Claims ABSTRACTOF THE DISCLOSURE Encapsulation of liquids with metal. A core liquid isdispersed in a carrier liquid in which it is essentially insoluble (oneof the liquids being aqueous), in a container whose surface is phobic tothe core liquid. Metallizing and reducing compounds are added.Nucleating metal is deposited at the interface between the liquids byintroducing a surfactant-type metal-organic compound of thehydrophobic-hydrophilic type having a more readily oxidizable metal ionthan the metal of the metallizing agent, so that molecules of thesurfactant align themselves at the interface and present their metalions to the aqueous liquid to nucleate deposition of metallizing ions.In one embodiment, the metallizing materials are disposed to deposit anoble metal at the interface, and the resulting noble-metal-coatedcapsules are subsequently over-coated with one or more layers of anon-noble metal by electrodeposition.

RELATED APPLICATION This application is a continuation-in-part of ourcopending U.S. patent application Ser. No. 117,059, filed Feb. 19, 1971,now abandoned.

BACKGROUND There is a growing demand for encapsulated liquids forapplications such as carbon-paper-less copy paper, cigarette filterwater release, etc. Additionally, there are now uses for encapsulatedliquids such as the electrically conductive capsules for use in theindicating coatings of copending patent application Ser. No. 11,418,filed Feb. 16, 1970, now abandoned, entitled Indicating Coating. Saidapplication has been replaced by a continuation filed Sept. 25, 1972,Ser. No. 291,690.

Such demands are currently met by processes such as those described inU.S. Pat. No. 2,800,458, B. K. Green, wherein a nonpolar liquid to beencapsulated is dispersed in a polar carrier liquid in which it isinsoluble. The coating material consists of a protein or gelatinousmaterial such as gelatin or a vegetable gum which is added to thecarrier liquid and caused to coagulate through the phenomenon ofsyneresis by adjustment of solution pH and/ or temperature or othersuitable means entrapping the nonpolar (i.e., oily) liquid to effectmicroencapsulation.

Other well known prior art means for encapsulating liquids include thesubstantial reverse of the above-described procedure. In this process anaqueous solution is dispersed in a nonaqueous-nonpolar solvent liquidcontaining dissolved hydrophobic polymerized material. A nonaqueousnonpolar liquid in which the polymerized material is insoluble is addedto the dispersion to cause the polymerized material to precipitate outof solution and form capsule walls around the aqueous phase. This methodis taught by U.S. Pat. 3,173,878.

Various other means for encapsulation include coating a solid materialand replacing the solid with a liquid by leaching as taught in U.S. Pat.3,460,972 and spray coating fluidized frozen liquids as taught in U.S.Pat. 3,202,- 533.

3,788,955 Patented Jan. 29., 1974 One of the most important requirementsfor encapsulated liquids relates to the integrity of the capsule wall.Nearly all of the above procedures provide capsule walls of organicmaterials that are inherently porous. Thus, the shelf life or periodduring which the capsules will effectively hold or retain the liquidcore is limited.

THE INVENTION We have now discovered a method whereby liquid cores maybe encapsulated with metals. A continuous metal case exhibitssubstantially no porosity and, consequently, our method providesliquid-filled capsules with greater shelf life than any of the presentlyknown encapsulation procedures.

We disperse the core liquid in, or form an emulsion of, this liquid witha carrier liquid in which the core liquid is insoluble or immiscible. Wethen add a metallizing material such as a silvering solution that isused to coat glass in the manufacture of mirrors and an appropriatereducing agent to affect appropriate reduction of the metallizingcompounds and make metal ions available for deposition.

As in the case of glass metallizing or silvering the interface betweenthe liquid (liquid we are encapsulating) and the carrier liquid must beactivated or deposition must be nucleated before capsule walls(silvering) will occur. In the silvering of glass, catalysts such as tinchloride are adsorbed onto the glass surface prior to treatment. The tinions being readily oxidizable are displaced by reducing silver ions atrandom sites on the glass surface nucleating the deposition of silverions. In the present instance, however, the usual catalytic metalcompounds such as tin chloride obviously cannot be applied to theinterface between the core liquid and the carrier liquid. Thus,catalytic nucleation of metallizing or the deposition of metal ions inthe conventional sense is not possible.

Where the liquid to be encpasulated is immiscible in water and thecarrier liquid is aqueous, we have found that such catalytic action maybe effected through the use of surfactants that consist of polarmetal-organic compounds. These compounds, like detergents, have ahydrophilic end (the organic end) and a hydrophobic end (themetal-containing end). The metal ion located at the hydrophilic end ofthe molecule in the present instance consists of a metal that is morereadily oxidized than the metal of the metallizing compound. Thus, thissurfactant functions as a catalyst in initiating deposition at theinterface between the core liquid and the carrier liquid since themolecule will align itself at the interface with its hydrophobic endtoward the liquid to be encapsulated and its hydrophilic end toward thecarrier, exposing the readily oxidizable metal ion to replacement with areduced metallizing ion to initiate deposition.

The catalytic surfactant of the present invention may be anymetal-organic compound (or molecule) having a hydrophilic part or endthat includes a metal that is more readily oxidizable than the metal tobe deposited (or reduced) and a hydrophobic part or end that will seekout the nonaqueous emulsion at the emulsion interface presumably toescape the water and thus expose the metal to oxidation. Themetal-organic compound must possess some solubility in water althoughthis may be slight since only a small amount of catalytic or nucleatingaction is generally required to effect encapsulation. For example, anymetal salt of an alkyl acid may be employed providing such salts meetsthe above-described parameters. Also, some aryl salts such as stannousbenzoate or tartrate may be employed in appropriate circumstances.Further, alkyl or aryl metal chelates may be used in some instances.

The most available metal-organic compounds or molecules for use inconjunction with the method of the present invention are the metal saltsof the fatty acids particularly those ranging in carbon from about 4carbon atoms to 18 carbon atoms. Such compounds that contain less than 4carbon atoms would tend to dissociate in the usual ammoniacalmetallizing solution while the limited solubility of those exceedingabout 18 carbon atoms would be very slight. Such compounds may besaturated or unsaturated since this parameter does not enter into thefunction of the addition.

We have had particular success in using stannous compounds (i.e.,stannous octoate Sn(O CC H as our catalytic surfactant, however, as setforth above, any metal salt may be employed so long as the metal is morereadily oxidizable than the metal of the metallizing salt.

We have found that the catalytic surfactant may be added either to thecore liquid or to the carrier liquid (or to both). Where making theaddition to the core liquid, it is, of course, most convenient to makethe addition prior to the formation of the emulsion. Where the additionis to be made to the carrier liquid, it can be made either before orafter the formation of the emulsion or the addition of the metallizingand metallizing-reducing additions.

The metal-organic hydrophilic-hydrophobic surfactant utilized inconjunction with the method of the present invention must also becompatible with the nonpolar liquid or liquid to be encapsulated. Bycompatible, we mean at least partially soluble and the liquid to beencapsulated cannot be of a type to interfere with proper alignment atthe emulsion liquid-liquid interface to nucleate metallizing. Forexample, if the liquid to be encapsulated has as great as or greateraffinity for the hydrophilic portion of the surfactant as the carrierliquid, it will not align itself at the interface in the desired manner.We have found that highly halogenated organic liquids such as carbontetrachloride and chloroform, though immiscible in water, are generallyincompatible with the usual hydrophobic-hydrophilic metal organicsurfactant.

Metallizing compositions or solutions are not confined to silveringcompositions or solutions although the greatest utilization of thiscoating technique is in coating glass to provide mirrors.

Most silvering solutions are comprised in part of an ammoniacal solutionof silver nitrate (usually containing some alkali metal hydroxide) plusa reducing solution which functions to convert the ammoniacal silver tothe metallic form.

Other well-known metallizing compositions or solutions include coppercoating baths which are very similar to silvering solutions. Forexample, one such solution, is disclosed in US. Pat. 2,939,804,Schossberger et al., which consists of 35 gl./l. of copper sulfate (CuSO-5H O) and 173 g./l. of sodium hydroxide (NaOH).

Still further commonly used metallizing solutions include gold,platinum, palladium, cobalt, and nickel compounds (for nickel compoundssee US. Pat. No. 3,420,-

680, Galla).

The reducing agent may be any material capable of reducing the metalcompound of the metallizing solution to render anions or positive metalions available for cationic deposition at the interface between the coreliquid and the carrier liquid. Common reducing agents for silveringsolutions are formaldehyde, Rochelle salts (sodium potassium tartrate),sugar, and hydrazine. The recommended reducing agent for theaforementioned copperizing solution is Fehlings solution.

The noble metals such as silver, gold, platinum, and palladium depositon the interface surface more readily than metals such as copper,nickel, and cobalt. The reason for this is that the known reducingagents and catalytic surfactants are far more efiicient in reducingthese metals to their elemental or metallic state than metals such asnickel and cobalt. However, it is economically highly desirable toeffect capsule walls of metals such' as' nickel and cobalt rather thanthe noble metals. An effective way of accomplishing the desired resultis to effect a small or minor coating of a noble metal (i.e., Au, Ag,Pt, and Pd) through the use of an appropriate metallizing solution,reducing agent, and catalytic surfactant and then over-coating the noblemetal coating with the desired metal coat. Since the capsules possess acoat of noble metal, the noble metal will itself nucleate deposition ofmetal from other metallizing solutions such as solutions for the depositof nickel, cobalt, and copper. Such a noble metal coat may be so thin asto be imperceptible and may be noncontinuous but will serve to nucleatemetal deposition from other metallizing materials.

Metallizing compounds and reducing agents may be added to the emulsionwith the addition of the catalytic surfactant in minor properties forthe limited deposition of a noble metal and, subsequently, metallizingcompounds and reducing agents may be added to the same emulsion ingreater proportions to effect a complete encapsulation with a non-noblemetal (for example, Ni, Cu, or C0). Any number of encapsulating metallayers may be effected in this manner.

Alternately, capsules thinly coated with a noble metal in the mannerdescribed above may be over-coated with one or more second coatings byconventional electroplating. For example, we have electroplated copperonto the surface of capsules of silver coated silicone by floating thecapsules on a copper sulfate bath and contacting the capsules with ahorizontal cathode plate.

for some applications, such as for use in the indicating coating of US.patent application Ser. No. 11,418, now abandoned, the core liquid maybe a liquid capable of carrying an electric current. For example, aconductive liquid may consist of a solution of ammonium chloride andglycerine. Such a solution may be dispersed in an aqueous solution andmetallize coated in the manner dedescribed above. Where the liquid oneproposes to encapsulate is not electrically conductive, it may berendered electrically conductive by incorporating a dispersion of carbonparticles therein. For example, we have rendered ethylene glycolelectrically conductive by making 2 percent, by weight, additions ofborax and 5 percent, by weight, SC Carbon (milled).

The particulate carbon addition may, of course, come from anyessentially elemental carbon source. For example fine lampblack is anexcellent source of powder for this application, however, granular orflake graphite can also be used. The particle size of the carbon can becritical and the carbon particles can be any size that will provideadequate electrical conductivity. Preferably, however, the carbon willbe at least fine enough to pass through a 50- mesh screen.

Where the liquid to be encapsulated is not electrically conductive, thecarbon may be dispersed therein by means of mechanical agitation. Theliquid then becomes a conductive liquid which is in turn dispersed inthe carrier liqiud. Appropriate surfactants can be added to theelectroconductive liquid to maintain the carbon dispersion andappropriate surfactants such as emulsifiers may be added for the carrierliquid to maintain the emulsion or dispersion of the conductomer liquidin the carrier during coating.

We have had surprising success in both maintaining the emulsion of theelectrically conductive liquid in the carrier liquid and in preventingthe carbon particles from separating from the conductive liquid byadding a single wetting agent (PC- Surfactnt, manufactured by 3M Companyor J. P. Stevens 915, both fluorocarbon detergents) to the carrierliquid that will perform this function.

Especially good results are obtained when the emulsion comprises also awetting agent that enhances the stability of the emulsion. The wettingagent typically comprises a surfactant that is at least slightly solublein both the core liquid and the carrier liquid, such as sodium laurylsulfate, a fluorocarbon detergent, or an alkyl phenyl polyethyleneglycol ether. It is also preferred that the materials be held in acontainer whose surface is phobic to the core liquid, and the emulsionmay beneficially comprise also a wetting agent that increases the phobiccharallowed to form liquid-liquid interfaces. A silver nitrate silveringsolution was mixed with the water phase of each test. A silveringsolution reducing agent (Rochelle Salts), when used, was also mixed withthe water phase. Varying surfactants (where used) were added to thewaterimmiscible liquid. The results are set forth in the followingtable:

TABLE I Silver nitrate Test number Water-immiscible liquid Surfactantsolution Rochelle salts Results 1 Mineral oil. No silvering. 2 oSilvering 3 do D0. 4 Dibutyl phthalate Do. 5 ..do D0. 6 No silvering.7... to Do. 8 Platinum chloride. Do. 9-.- Silvering. l0 ..dn 50 Yes N0 osilvering. 11 do Tributyl tin chloride.-. Yes Yes Silvering, 12 do NoneYes..- Yes No silvering. 1% rln Tributyl tin chlonde Yes No.. Do, 14 doButyl titanate Yes Yes. Silvering. 1H dn dn Yes No.. No silvering. 16 dnBenzylaldehyde Yes..- Yes. D 17 dn Butyraldehyde..-.. Yes... Yes. Do. 13(in Benzylaldehyde Yes No Do. 19 d Butyraldehyde Y No Do. 20 d Tributyltin chloride Yes Butyraldehyde Slight silvering; 21 g do do YesBenzaldehyde Do.

1 A silicone rubber catalyst, manufactured by 2 A silicone rubbercatalyst, manufactured by acter of the container surface. This wettingagent typically comprises a surfactant that is soluble in the carrierliquid, such as alcohol sulfates, sodium salts, and alkylaryl sulfonateswhere the carried liquid is aqueous, and such as fluorocarbon andfluorophosphate detergents where the carrier liquid is nonaqueous. Wherethe core liquid comprises water, the container surface preferablycomprises polyethylene, polytetrafluoroethylene polystyrene, or otherpolymerized organic plastic, and the carrier liquid preferably consistsessentially of a substantially waterinsoluble oil, typically an organicoil such as toluene or mineral oil. The metallizing materials typicallycomprise essentially silver nitrate; ammonia; magnesium sulfate; and, asa reducing compound, (Rochelle salts; and the metal-organic surfactantcompound typically consists essentially of stannous octoate. In certainuses such as in marking or covering markings, the diameters of at leastabout 90 percent of the capsules should be about to 150 microns, with anaverage diameter of about to 125 microns.

EXAMPLES (l) cc. water was placed in a 250 ml. beaker. (2) 15 cc. of 1%,by weight, FC-95 surfactant (3M Company) was added. (3) About 2 cc. ofsilicone oil containing carbon particles was added. (4) A stirrer wasused to disperse the oil droplets in the water. The surfactant preventedthe droplets from coalescing and the carbon from separating from theoil. (5) Three drops of Dow Corning Corporation 502 silicone rubbercatalyst was added. The active ingredient of this catalyst is tinoctoate. (6) Silvering solution and reducing solution concentrates wereadded to form a silver-mirror coating solution. (7) Stirring wascontinued for 30 minutes and the silver-coated droplets of oil werewashed by decanting several times with water containing the surfactant.('8) Several of the silver-coated droplets were copper electroplated byfloating them on an acid copper sulfate bath and contacting them with ahorizontal cathode plate. After plating for a short time, themetal-coated spheres sank to the bottom of the tank.

A series of tests were conducted to determine the 0perability of variousmaterials when used in conjunction with the method of the presentinvention. In each of these tests water immiscible liquids were mixedwith water and ow Corning Company, the active ingredient of whichconsists of stannous octoate. & T Chemicals, Inc., the active ingredientof which consists of stannous octoa to.

From the above data, it is obvious that to effect metal encapsulation inaccordance with the method of the present invention one must employ ametal-organic surfactant of a metal that is more readily oxidizable thanthe metallizing (silvering) metal. The surfactant must be of thehydrophilic-hydrophobic type and must be compatible with the nonpolarliquid.

FURTHER EXAMPLES (A) Encapsulating oil droplets with silver (1) 250 ml.of a solution of a wetting agent such as 350 mg. of surfactant FC-95 (3MCompany) per liter in distilled water, is prepared. This is a preferred,but optional, step which provides the wetting agent recited in some ofthe claims. (2) 4 ml. of light mineral oil are dispersed in the solutionwith vigorous stirring for about 5 minutes. (3) ten drops (about 350mg.) of a stannousoctoate catalyst such as T-9 (M&T ChemicalsCorporation) are added to the oil-water dispersion with reduced stirringfor about 2 minutes. This step provides the metalorganic surfactantcompound recited in the claims. (4) Sixty ml. of an equivolume mix ofsilver-reducer concentrates are added to the oil-catalyst-waterdispersion (about 1.3 g. of Ag/ 310 ml.) with mild stirring for about 20minutes. The first four steps may be carried out in any other convenientorder, or substantially simultaneously, if desired. (5) Stirring isstopped and the dispersion is allowed to settle. Because the coating isvery thin, the silver-coated droplets produced appear light gray-blackto the naked eye. (6) About ml. of the dispersion containing coated oildrops are decanted into ml. of a solution similar to that of Step (1)(about 300' mg. 0g FC-95 per liter). This is is another preferred, butoptional, step for providing a wetting agent. (7) A second 60 ml. mix ofthe silver-reducer concentrates is added to the decanted dispersion mix,to complete the silvering reaction after standing for at least about anhour. To increase the thickness of the silver wall, this step may berepeated. (8) Most of the capsules now have a metallic silverappearance. (9) The capsules are rinsed, collected on filter papers, andair dried. (10) Where stronger coatings are desired, the capsules arefurther coated with copper as in the other examples or in any otherconvenient manner.

(B) Encapsulating water-containing droplets (1) To a 500 ml. capacitypolyethylene bottle the following reagents are added:

(a) About 50 ml. toluene. (Mineral oil can be used in place of part orall of the toluene.)

(b) About 0.1 gram stannous octoate (M&Ts T-9).

() About 0.1 gram surfactant FC-95 (3M). This is an optional material,providing the wetting agent recited in some of the claims.

(d) About 0.5 ml. of a silvering solution. A typical silvering solutioncontains about 0.25 ml. of AgNO (70 g./1.) with NH OH (about 80 ml./l.),and about 0.25 ml. 425 g./l. Rochelle salts with 30 g./l. MgSO-7H O. Itmay be conveniently injected by hypodermic needle and syringe to producesmall droplets.

1(2) The mixture is allowed to stand for about 2 to 24 ours.

Tests with Example (B) show that for best yields the surface of thecontainer should be phobic to the liquid to be encapsulated. When wateris the core liquid a hydro phobic material such as polyethylene,polytetrafluorethylene, polystyrene, or other polymerized organicplastic is satisfactory. Glass and metal are not.

The following additional steps are also recommended: (3) The resultingsilver coated spherical capsules are poured onto an electroless copperplating solution comprising about 15 g./l. copper nitrate (CuNO -3H O),1O g./l. sodium bicarbonate (NaHCO' 30 g./l. Rochelle salts, and 20g./l. sodium hydroxide (NaOH), but without the usual formaldehydereducer. (4) The mixture is allowed to stand until the toluene hasevaporated. This typically requires about one to twenty-four hours. (5)About 100 ml. per liter of formaldehyde (37-38% HCHO) are added. (6) Themixture is allowed to stand for about one to two hours. (7) The copperplated spheres are removed from the plating solution.

What is claimed is:

1. The process of forming capsules having a liquid core and a metal casecomprising:

(a) forming an emulsion of the core liquid in a carrier liquid, one saidliquid being aqueous and the other being substantially water-immiscibleand the emulsion being held in a container whose surface is phobic tothe core liquid;

(b) introducing metallizing materials, including a reducing compound,into said emulsion; and

(c) nucleating metal deposition from said metallizing materials at theinterface between said core liquid and said carrier liquid byintroducing into said emulsion a metal-organic surfactant compound thatis at least partially soluble in both said core liquid and said carrierliquid and which is compatible with said water-immiscible liquid, themetal containing part of said surfactant being philic to said aqueousliquid and the nonmetal part being phobic to said aqueous liquid so thatthe molecules of said surfactant will align themselves at the interfaceof said core and carrier liquids with the philic parts directed to theaqueous liquid, the metal of said surfactant being more readilyoxidizable than the metal of said metallizing compound in theenvironment of the emulsion so that at least some of the metal ions ofthe surfactant will reduce metal ions of said metallizing compound to ametallic state to nucleate metallizing of the interface between saidcore liquid and said carrier liquid;

((1) wherein said metallizing materals provide at least one metalselected from the group consisting of Ag, Cu, Au, Pt, Pd, Co, and Ni andsaid surfactant consists essentially of butyl titanate or of a stannoussalt of a fatty acid having from about 4 to 18 carbon atoms.

2. The method of claim 1 wherein said carrier liquid consistsessentially of water and said core liquid consists essentially of asubstantially water-insoluble oil.

3. The process of forming capsules having a liquid core and a metal casecomprising:

(a) forming an emulsion of the core liquid consisting essentially of asubstantially water-insoluble oil in a carrier liquid consistingessentially of water, said liquids being substantially immiscible in oneanother;

(b) introducing metallizing materials, including a reducing compoundinto said emulsion, said metallizing materials providing an ammoniacalsolution of a silver compound and a reducing material that functions toconvert the silver to the metallic form; and

(c) nucleating metal deposit from said metallizing materials at theinterface between said core liquid and said carrier liquid byintroducing into said emulsion a metal-organic surfactant compoundconsisting essentially of a stannous salt of a fatty acid having fromabout 4 to 18 carbon atoms that is at least partially soluble in bothsaid core liquid and said carrier liquid and which is compatible withsaid core liquid, the metal containing part of said surfactant beingphilic to said carrier liquid and the nonmetal part being phobic to saidcarrier liquid so that the molecules of said surfactant will alignthemselves at the interface of said core and carrier liquids with thephilic parts directed to the carrier liquid, the metal of saidsurfactant being more readily oxidizable than the metal of saidmetallizing compound in the environment of the emulsion solution so thatat least some of the metal ions of the surfactant will reduce metal ionsof said metallizing compound to a metallic state to nucleate metallizingof the interface between said core liquid and said carrier liquid.

4. The method of claim 3 wherein said core liquid consists essentiallyof a silicone oil.

5. The method of claim 4 wherein said silver compound consists of silvernitrate.

6. The method of claim 4 wherein said silicone oil is provided with adispersion of carbon particles therein that are disposed to render saidoil electrically conductive.

7. The method of claim 2 wherein a wetting agent is added to saidemulsion to maintain said emulsion.

8. The method of claim 6 wherein a wetting agent is added to saidemulsion to maintain said emulsion and to maintain the dispersion ofsaid carbon particles.

9. The process of claim 1 wherein said metallizing materials aredisposed to deposit a noble metal at said interface and saidnoble-metal-coated capsules are subsequently over-coated with one ormore layers of a nonnoble metal.

10. The process of claim 9 wherein said noble metal is at least onemetal selected from the group consisting of Ag, Au, Pt, and Pd and saidnonnoble metal is at least one metal selected from the group consistingof Cu, Ni, and Co.

11. The process of claim 10 wherein the noble-metalcoated capsules arecoated with the nonnoble metals by exposure to one or more metallizingsolutions of the nonnoble metals so that the noble-metal coatings act ascatalysts for deposition of one or more of the nonnoble metals.

12. The process of claim 10 wherein the noble-metalcoated capsules arecoated with one or more of the nonnoble metals by electrodeposition in aplating solution of the nonnoble metal.

13. The method of claim 1 wherein said surfactant is added to said coreliquid prior to forming said emulsion.

14. A process as in claim 1, wherein the emulsion comprises also awetting agent that enhances the stability of the emulsion.

15. A process as in claim 1, wherein the emulsion comprises also awetting agent that increases the phobic character of the containersurface.

16. A process as in claim 1, wherein the core liquid comprises water andthe container surface comprises polyethylene, polytetrafluoroethylene,polystyrene, or other polymerized organic plastic.

17. A process as in claim 1, wherein the core liquid consistsessentially of Water and the carrier liquid consists essentially of asubstantially water-insoluble oil.

18. A process as in claim 17, wherein the carrier liquid consistsessentially of toluene.

19. A process as in claim 17, wherein the carrier liquid consistsessentially of mineral oil.

20. A process as in claim 17, wherein the metallizing materials compriseessentially silver nitrate; ammonia; magnesium sulfate; and, as areducing compound, Rochelle salts.

21. A process as in claim 20, wherein the metal-organic surfactantcompound consists essentially of stannous octoate.

22. A process as in claim 14, wherein the wetting agent comprisesessentially a surfactant that is at least slightly soluble in both thecore liquid and the carrier liquid.

23. A process as in claim 15', wherein the wetting agent comprisesessentially a surfactant that is soluble in the carrier liquid.

References Cited UNITED STATES PATENTS 2,757,104 7/1956 Howes ll7l60 R X3,390,026 6/1968 Cerych et a1. 117--160 R X 3,406,119 10/1968 Kosar etal. 252316 3,468,662 9/1969 McCune, Jr. Z52313 R X 3,503,783 3/1970Evans 252-3l6 X RICHARD D. LOVERING, Primary Examiner US. Cl. X.R.

117-41 R, A, 100 B, R, 217, 227; 20438 B; 252-616; 2644

